This invention relates to television synchronizing pulse generating apparatus.
The train of pulses used to synchronise television picture origination equipment and television receiving equipment is commonly known as Mixed Syncs. (U.K.) or Composite Syncs. (U.S.A.). This pulse train consists of three types of pulses as follows:-
A. Line Syncs. to synchronise the horizontal scanning circuits. PA1 B. Equalising pulses to ensure correct interlacing of odd and even fields. PA1 C. Broad Pulses to synchronise the vertical scanning circuits.
Such pulse trains are produced by known generators, the various pulses in the train being generated in a sequence dependent on the system in which they will be used (e.g. 525 line or 625 line).
It is often desirable to provide an addition to the normal mixed sync. pulses a further set of mixed syncs. which lead (in time) the normally used mixed syncs. by a period of a few lines. An existing solution to this problem is to regenerate the complete mixed sync. train via phase locked loop oscillators for example which can provide the advanced timing information. This is an expensive solution since it calls for a repetition of the major part of the equipment known generally as a television sync. pulse generator which is used to generate the normal mixed sync. pulses.
In some applications it is not necessary for the additional pulse train to be identical to the normal mixed sync. pulse train, e.g. when the additional advanced pulses are used merely as a synchronising signal for a video tape recorder. In such applications a simplified generator system could be used.